Summary of "Complete Synchronous Machine | In One Shot | Electrical by Raman sir"

Summary of "Complete Synchronous Machine | In One Shot | Electrical by Raman sir"

Main Ideas and Concepts Covered:

  1. Introduction to Synchronous Machines:
    • Definition: Synchronous Machines are AC machines operating at a speed synchronous with supply frequency.
    • Types: They function as both generators (convert mechanical energy to electrical energy) and motors (convert electrical energy to mechanical energy).
    • Applications: Widely used in power generation (hydro, thermal, nuclear plants) and industrial power factor correction.
  2. Basic Construction:
    • Stator: Similar construction in synchronous and induction machines, made of laminated silicon steel to reduce eddy current and hysteresis losses.
    • Armature Core: Contains slots for Armature Winding; slots reduce harmonics and mechanical stress.
    • Armature Winding: Two types discussed:
      • Concentrated winding: All coil turns are concentrated in one slot.
      • Distributed (Distributor) winding: Spread across multiple slots to reduce harmonics and improve mechanical balance.
    • Rotor: Two main types:
      • Salient Pole Rotor (projected poles, short axial length, large diameter, used in low-speed applications like hydro plants).
      • Cylindrical (non-salient) Rotor (smooth surface, uniform air gap, longer axial length, used in high-speed applications like thermal and nuclear plants).
  3. Winding Details and Factors:
    • Full pitch vs. Short pitch winding:
      • Full pitch winding has coil span equal to pole pitch; pitch factor = 1.
      • Short pitch winding reduces coil span to save conductor material and reduce harmonics but decreases induced EMF.
    • Important winding factors:
      • Pitch factor (Kc) = cos(α/2), where α is the coil span angle.
      • Distribution factor (Kd) = sin(mβ/2) / (m sin(β/2)), where m is number of slots per pole per phase and β is slot angle.
      • Winding factor = Kc × Kd.
    • Harmonics elimination by proper coil span selection.
  4. Electromagnetic Principles:
    • Faraday’s Law: EMF induced in conductors due to changing magnetic flux.
    • Fleming’s Right-Hand Rule for generators (EMF direction) and Left-Hand Rule for motors (force direction).
    • Relationship between mechanical angle and electrical angle: Electrical angle = (Number of poles / 2) × Mechanical angle.
    • Frequency-speed-pole relation: \( f = \frac{P \times N}{120} \), where f = frequency, P = number of poles, N = speed in RPM.
  5. Armature Reaction:
    • Effect of armature current on main field flux (main MMF).
    • Depends on load power factor:
      • Unity power factor: Armature reaction is cross magnetizing (90° lagging).
      • Lagging power factor: Armature reaction demagnetizes main field (flux reduction).
      • Leading power factor: Armature reaction magnetizes main field (flux increase).
    • Vector diagrams used to explain interaction of main field MMF and armature reaction MMF.
    • Resultant MMF affects terminal voltage and voltage regulation.
  6. Equivalent Circuit and Phasor Diagrams:
    • Development of synchronous machine equivalent circuit incorporating armature resistance, leakage reactance, and synchronous reactance.
    • Phasor diagrams illustrate relationships between induced EMF, terminal voltage, armature current, and power factor angle.
    • Voltage regulation explained based on load conditions.
  7. Losses and Resistances:
    • Armature Winding resistance measured using DC methods.
    • AC resistance is higher than DC resistance due to skin effect (current crowding near conductor surface).
    • Skin effect increases with frequency and conductor diameter.
    • Leakage flux types:
      • Slot leakage flux (flux around conductors in slots).
      • Air gap leakage flux (flux passing through air gap but not linking all conductors).
      • End connection leakage flux (flux linked with overhang portions of winding).
    • Leakage reactance caused by leakage flux leads to voltage drop.
  8. Field Excitation and Exciters:
    • Field winding placed on rotor, supplied with DC excitation.
    • Excitation methods:
      • Separate DC generator (pilot exciter and main exciter).
      • Static excitation (using rectifiers and transformers).
      • Brushless Excitation (eliminates brushes and slip rings using rotating rectifiers).
    • Use of permanent magnets in small Synchronous Machines or pilot exciters.
    • Advantages of placing Armature Winding on stator (stationary) and field winding on rotor (rotating):
      • Easier insulation for high voltage Armature Winding.
      • Reduced mechanical stresses on winding.
      • Simplified cooling.
  9. Starting and Operation:
    • Synchronous motors require synchronization with supply frequency.
    • Damper windings

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